Thermomechanical Stresses in Silicon Chips for Optoelectronic Devices (original) (raw)
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Measurement of the state of stress in silicon with micro-Raman spectroscopy
Journal of Applied Physics, 2004
Micro-Raman spectroscopy has been widely used to measure local stresses in silicon and other cubic materials. However, a single (scalar) line position measurement cannot determine the complete stress state unless it has a very simple form such as uniaxial. Previously published micro-Raman strategies designed to determine additional elements of the stress tensor take advantage of the polarization and intensity of the Raman-scattered light, but these strategies have not been validated experimentally. In this work, we test one such stategy [S. Narayanan, S. Kalidindi, and L. Schadler, J. Appl. Phys. 82, 2595 (1997)] for rectangular (110)and (111)-orientated silicon wafers. The wafers are subjected to a bending stress using a custom-designed apparatus, and the state of (plane) stress is modeled with ABAQUS. The Raman shifts are calculated using previously published values for silicon phonon deformation potentials. The experimentally measured values for xx , yy , and xy at the silicon surface are in good agreement with those calculated with the ABAQUS model.
Journal of Raman Spectroscopy, 2009
Mechanical stresses in microelectronics and micro-electromechanical systems may influence the reliability of applications and devices. The origin of the stresses can be because of the joining of dissimilar materials with regard to the thermal expansion coefficient, electromigration or the deposition process utilized. Stresses can lead to delamination, crack formation and stress migration and therefore to a failure of the device. Identifying the locations of highest stresses in a device is crucial for reliability improvement. Currently, both Laue X-ray micro diffraction and convergent-beam electron diffraction are able to locally determine the stresses in thin metal films. Here, we propose a modified method of indirect Raman microspectroscopy to measure stresses with a lateral resolution in the submicrometer range at a laboratory scale. The method encompasses the crystallization of an amorphous silicon layer by local laser annealing and its subsequent usage as a strain gage. Stresses in an aluminum thin film were determined as a function of temperature. In addition to the average stress, the stress distribution could be monitored.
Residual Stress in Silicon Caused by Cu-Sn Wafer-Level Packaging
Volume 1: Advanced Packaging; Emerging Technologies; Modeling and Simulation; Multi-Physics Based Reliability; MEMS and NEMS; Materials and Processes, 2013
The level of stress in silicon as a result of applying Cu-Sn SLID wafer level bonding to hermetically encapsulate a highperformance infrared bolometer device was studied. Transistors are present in the read out integrated circuit (ROIC) of the device and some are located below the bond frame. Test vehicles were assembled using Cu-Sn SLID bonding and micro-Raman spectroscopy was applied on cross sectioned samples to measure stress in the silicon near the bond frame. The test vehicles contained cavities and the bulging of the structures was studied using white light interferometry. The test vehicles were thermally stressed to study possible effects of the treatments on the level of stress in the silicon. Finite element modeling was performed to support the understanding of the various observations. The measurements indicated levels of stress in the silicon that can affect transistors in regions up to 15 µm below the bond frame. The observed levels of stress corresponded well with the performed modeling. However, no noticeable effect was found for the ROIC used in this work. The specific technology used for the fabrication of the ROIC of a MEMS device is thus decisive. The level of stress did not appear to change as a result of the imposed thermal stress. The level of stress caused by the bond frame can be expected to stay constant throughout the lifetime of a device.
Journal of Applied Physics, 1998
A method is described to calculate the Raman spectrum from a nonuniformly strained sample taking into account the effects that arise due to finite depth of penetration and diameter of the laser beam. Both the parallel and the focused beams are considered. The case of stress in a Si substrate decaying monotonically with depth z (rapidly near the interface and slowly at larger depths) is considered in detail. The predicted Raman shifts are found to be sensitive to both the distribution of stress and to the absorption coefficient alpha for the laser light wavelength used. It is found that light scattered from distances much larger than 1/alpha still contribute significantly to the observed Raman spectrum. The observed shift in the peak of the spectrum does not correspond to the stress close to the interface. If the stress decays more rapidly than the light intensity, the Raman line that originates from the unstrained lower part of the substrate dominates. For transparent material (alpha=0) and unfocused beam the Raman spectrum consists of only the unstrained Si line; the contribution to Raman line from the strained interface region is completely masked. For measurements of stresses near the interface short wavelength light with an absorption depth of 5-10 nm is recommended. The calculated and observed Raman shifts in a local oxidation of silicon (a processing technique for isolation) with polysilicon buffer between the nitride stripe and the Si substrate are compared. The agreement between the calculated and the observed Raman shifts is very good. The salient points of our approach which enabled us to obtain this agreement are: We took into account the effects of laser beam width, penetration depth, and focusing; we included the stresses in the polysilicon layer and near the polysilicon/silicon interface, and we included contributions from large depths.
Microscale Measurement of Stresses in a Silicon Flexure Using Raman Spectroscopy
MRS Proceedings, 2002
ABSTRACTWe report the use of Raman spectroscopy to characterize the bending stresses in a deep reactive-ion etched, single-crystal, silicon flexure of length 2950 μm, width 480 μm, thickness 150 μm, and fillet radius 65 μm, subjected to a tip displacement of 69.5 μm. The spectral resolution of the measurement was 0.02 cm-1, which corresponds to a stress resolution of ∼10 MPa, and the spatial resolution was ∼1 μm. Line scans were performed across the thickness, at several locations along the length, of the flexure. The changes in the Raman shift were converted to stress values, assuming a uniaxial stress state, without the use of any fitting parameters. A comparison of the measured values with the predictions of analytical and numerical models indicates agreement to within 25–35 MPa (or ∼15%) at locations sufficiently distant from the root. At the root itself, the complex nature of the stress distribution precludes unambiguous stress determination using spectroscopic measurements.
Acta Mechanica Sinica, 2018
The requirement of stress analysis and measurement is increasing with the great development of heterogeneous structures and strain engineering in the field of semiconductors. Micro-Raman spectroscopy is an effective method for the measurement of intrinsic stress in semiconductor structures. However, most existing applications of Raman-stress measurement use the classical model established on the (001) crystal plane. A non-negligible error may be introduced when the Raman data are detected on surfaces/cross-sections of different crystal planes. Owing to crystal symmetry, the mechanical, physical and optical parameters of different crystal planes show obvious anisotropy, leading to the Raman-mechanical relationship dissimilarity on the different crystal planes. In this work, a general model of stress measurement on crystalline silicon with an arbitrary crystal plane was presented based on the elastic mechanics, the lattice dynamics and the Raman selection rule. The wavenumberstress factor that is determined by the proposed method is suitable for the measured crystal plane. Detailed examples for some specific crystal planes were provided and the theoretical results were verified by experiments.
2008
Residual mechanical stress is currently among the most important parameters for improving processing yields and it will become increasingly important in view of the targeted decrease in the wafer or thin film thicknesses to reduce processing costs. A technique that is intensively used for analysing stress states at the micrometer scale in semiconductors is micro-Raman spectroscopy. Several stress-tensor components can be obtained separately using polarized laser light for the µ-Raman measurements or average stresses when using unpolarized light. We have found inhomogeneous stress distributions including local peak compressive and tensile stresses at (sub)grain boundaries and in areas with high concentrations of extended lattice defects. These stresses most probably form during the different heating and cooling processes of the multicrytalline silicon block and ribbon casting or during the laser melting and re-crystallization of amorphous silicon layers on thermally mismatched glass substrates. The possible mechanisms of stress formation and relaxation are discussed.
Japanese Journal of Applied Physics, 2012
The mechanical stresses in Si metal-oxide-semiconductor field-effect transistors (MOSFETs) were evaluated by polarized UV Raman spectroscopy measurements and stress simulations. To calibrate stress parameters of the materials used in the Si MOSFETs, we compared measured and simulated Raman frequency shifts on the cleaved Si(110) surfaces of the MOSFETs. Consequently, we extracted intrinsic stress values of À400 MPa for a SiO 2 , À200 MPa for polycrystalline Si (poly-Si), 700 MPa for Ni silicide, 1250 MPa for a SiN tensile stress liner, and À3500 MPa for a SiN compressive stress liner by finding good agreement between the measured and simulated Raman shift distributions. To verify our stress simulation, we investigated the source/drain width dependences of Raman frequency shifts near the channel regions of Si MOSFETs by top-view Raman measurements. The calculated Raman frequency shifts agreed well with the results of polarized Raman measurements in terms of not only relative tendencies but also absolute Raman shift values.
Visualizing stress in silicon micro cantilevers using scanning confocal Raman spectroscopy
Microelectronic Engineering, 2008
We report on the determination of surface stress in a resonantly oscillating silicon micro cantilever using confocal Raman spectroscopy. Focusing on the optical phonon line of silicon allows one to determine the lateral distribution of mechanical stress. However, the Raman shift caused by mechanical stress can be concealed by thermally induced Raman shifts and line-broadenings. Both effects are intrinsic to the micro Raman measurement which uses a strongly focused laser beam in a confocal microscope. In order to unravel the different contributions, we use a practical analytical method for the compensation based on reference measurements on a heated silicon wafer of the same crystal orientation. As an example, the structure of the micro cantilever was specially weakened by introducing a rectangular hole in the center of the lever. After compensation of the thermally induced shift, the true mechanical stress can be visualized as shown for a stress maximum of the cantilever driven at its second flexural eigenmode.